In the U.S. the number of obese women entering pregnancy has more than doubled in the past 30 years. Pregravid obesity alone however is not the only cause for concern since two-thirds of obese women gain weight in excess of the 2009 IOM recommendations and attempts to manage gestational weight gain to date have failed. To improve weight management of obese pregnant women, there is a critical need to deliver specific evidence-based recommendations on energy intake and energy expenditure (physical activity); the two primary determinants of weight gain in non-pregnant individuals. As an ancillary study to LIFE-Moms (Lifestyle Interventions in Expectant Moms Study) we will evaluate energy intake and energy expenditure during pregnancy (13 to 37 weeks) and 12 months postpartum in 80 obese women randomized to receive an intensive lifestyle intervention to manage gestational weight gain. We will test the hypothesis that obese pregnant women with weight gain above the IOM guidelines, 'High Gainers', will have increased energy intake but no evidence for changes in energy expenditure after adjustment for the weight gained when compared to women with appropriate gestational weight gain, 'Normal Gainers'. The primary outcome variables are 1) energy intake during pregnancy and 12 months postpartum measured with the energy balance method and with a mathematical model of maternal energy intake 2) the free-living energy expenditure and sleeping metabolic rate (absolute and adjusted for maternal body composition and fetal size) during pregnancy. Secondary outcomes include measurement of changes in physical activity and substrate oxidation, determinants of energy intake including fasting concentrations of leptin, total ghrelin, peptide YY, cholecystokinin and determinants of energy expenditure including urinary epinephrine and norepinephrine, fasting concentrations of T3, T4 and TSH.